1. Field of the Invention
The present invention relates to a semiconductor device and a chip carrier and, more particularly, a structure of a temperature sensor portion of the semiconductor device, for example, a structure of a thermistor element portion employed in temperature control of a laser chip of a semiconductor light emitting device as the major application mode.
2. Description of the Prior Art
In order to control the temperature of the laser chip in operation, for example, a thermistor is brazed to a ceramic carrier onto which a semiconductor light emitting element, e.g., a laser chip, is mounted, as shown in FIG. 1.
In FIG. 1, a rectangular first conductive pattern 102a and an L-shaped second conductive pattern 102b are formed in a first region that is positioned near one end on a major surface of a ceramic carrier 101. Also, a rectangular third conductive pattern 102c is formed in a second region that is positioned near the other end on the major surface.
A lower electrode 103a of the laser chip 103 is connected to such second conductive pattern 102b by a conductive brazing material 104, and also a first gold wire 105a is connected to such second conductive pattern 102b by the bonding. Second and third gold wires 105b, 105c that relay the first conductive pattern 102a are electrically connected to an upper electrode 103b of the semiconductor laser 103.
Also, a thermistor 106 is connected to the third conductive pattern 102c, so that the temperature is sensed in response to change in its resistance.
The thermistor 106 has first and second electrodes 106b, 106c formed on a major surface of a ceramic substrate 106a, and a thermistor element 106d connected to these first and second electrodes 106b, 106c. The thermistor having such structure is set forth in Patent Application Publication (KOKAI) Hei 6-61012, for example.
Then, a bottom surface of the ceramic substrate 106a is connected to the third conductive pattern 102c via a solder 107. Also, fourth and fifth gold wires are bonded to the first and second electrodes 106b, 106c respectively and then extended electrically to the outside therefrom. In this case, the third conductive pattern 102c is formed to improve the adhesiveness between the ceramic substrate 106a and the ceramic carrier 101.
However, in the above structure, a thermal resistance of a solder 107, that is interposed between the ceramic carrier 101 and the thermistor element 106d, is changed time-dependently due to the change in microstructure or the progress of crack caused by the solder creep after the semiconductor light emitting device is operated.
Therefore, the resistance value of the thermistor element 106d to sense the temperature of the laser chip 103 is changed with the lapse of the operation years of the semiconductor light emitting device.